Duchenne muscular dystrophy (DMD) is an X-linked recessive disease of muscle characterized by a progressive loss of functional muscle mass, which is replaced with fibrofatty tissue. Historically, boys with DMD lose the ability to walk between the ages of 8-12 years, due to progressive weakness of the quadriceps coupled with the development of contractures at the hip, knee and ankle. This progressive loss in function necessitates individuals with DMD to spend less time walking and more time in wheelchairs, leading to the development of spinal deformities. Recently, corticosteroids have been shown to reduce the expected loss of muscle strength, extend the time that ambulation and standing are maintained, and minimize or eliminate spinal deformity in individuals with DMD; yet, the side effects of such treatment preclude use in some patients. To date, differences in gait patterns and other markers of disease progression between boys on corticosteroids and those not utilizing such treatment have not been objectively quantified. This lack of knowledge is a major obstacle to determining the most effective treatment for subsets of boys with DMD.